Bob Ivins, managing director of comScore Europe, said "Many of the sites experiencing the fastest growth today are the ones that understand their audience's need for expression and have made it easy for them to share pictures, upload music and video, and provide their own commentary, thus stimulating others to do the same. It is the classic network effect at work."

*eBay is excluded from list of user-generated content sites because it is primarily a retail site.

Collectively, the leading UGC sites draw more frequent visits than non-UGC sites (4.2 vs. 3.5 average usage days per month), longer periods of engagement (79.9 vs. 33.2 average minutes per visitor), and more pages viewed (217 vs. 52 average pages per visitor).

Users of the top social networking sites demonstrate particularly high levels of engagement, with visitors to MySpace.com and Bebo.com averaging at least 5 usage days, 2 hours of use, and 300 pages viewed per visitor during July.

"... it is clear that UGC sites - and in particular social networking sites - represent potentially fertile ground for advertisers and marketers," continued Mr. Ivins. "... The challenge... is to determine effective ways to integrate (key messages) while maintaining a positive user experience."